Why do people save used cooking oil?

My roomate does this and it was all great until she poured the dirty oil back into the bottle with my clean oil. Why does she insist on saving used cooking oil?

Well, I dont want to tell her how to cook her food but I just dont understand why she would rather dirty MY clean cooking oil rather throw away her dirty cooking oil. If it was her clean cooking oil I would not have a problem. I think I am going to go find her a mason jar to put it in. Because I think I may have thrown the jar that she usually keeps it in, in the trash.

it's recyclable.
old tradition.
you will just have to label your oil bottle
or give her one labeled "for recycled oil"

ok that is just NASTY! I save bacon grease to cook in later or to season things like greens or beans or green beans but it has its own container in the fridge i would never dream of reusing like vegetable oil and Never would i combine the used with the new in the container what if you wanted to bake a cake? it would taste like whatever was cooked in the dirty grease yuck!

Ewwww! Ewwww! Ewwww! Why?! My mom use to do that when I was a child! That's so gross! What the heck?! You should tell girlfriend that cooking oil isn't that expensive. Heck, I'll do her one better. I'll send her some Pam! Ewwwww! I can't believe she does that? Gross! ( o _ o ) Could you wack her in the forehead for me please. : )

This was common a few years ago. That is why I always get my toast at cafes dry. They brush it with used grease.

That's so disgusting! My Mum used to do that when I was little. If she fried fish, she would save the oil and cook the NEXT batch of fish in it. Ew. She would also save oil and drippings from frying various meats and then use the oil to "flavor" her vegetables. (ick!) No wonder sister-girl had a heart attack!

Some people save it to use the flavor from the previous meal again. However, most people save used cooking oil in another container. I don't recommend mixing the new with the used.